Naw man its really easy. Just go up to Best Buy, Circut City, Audio King, wherever yo uwant to. And get a wiring harness for your G20.. make sure its for the right year etc.
After that all you do is match the wires on the harness to the wires on the head unit. Red on the harness connects to red on the head unit. Yellow on the harness connects to yellow on the head unit. Its really smiple and easy to do.
Then you plug it in and there ya go.